Radio tube testing apparatus



April 4 .v. H. LAUGHTER 2,196,466

RADIO TUBE TESTING APPARATUS v Filed April 5, 1937 '2 Sheets -Sheet 1 aff/1%. (4a 575/ 6 April 9, 1940. v. H. LAUGHTER 2,196,466

RADIO TUBE TESTING APPARATUS Filed April 5, 1937 2 Sheets-Sheet 2 IHHIHH'HHH Patented Apr. 9, 1940 a Testing'devices are usually so arranged that the indicator thereof may be calibrated by testing a l0 Victor H. Laughter, Shelby County; Tenn, assignor of one-half to Harry. T. Wilson, Memphis, Tenn. 1

' ApplicationApril' s, 1937,.Sefial No. 135,025

. This invention pertains to a method and"ap paratus for testing radio tubes in order to determine whether or not their] characteristics are such as to. render them suitable for use.

In the manner of testing radio tubes employed heretofore the simple emission test has been depended upon to indicate the quality or the tube.

normal tube, and thereafter tubes to] be tested are simplycompared with the normal calibrating tube. Such tests are often'unreliable because difierent in their emission characteristics.

the difierent makes of radio tubes are. widely tubes of the same type but of different makes may show up very difierently on such a test,

one tube showing a very high emission and the other a considerably lower value, although both are good tubes and suitable for-use-in a radio set. Under previous'methods of testing .such a low-reading tube might be discarded as bad according to the tests indication.

One of the objects of this invention, therefore, is to provide a method and apparatus whereby bad tubes may be segregated from good tubes in spite of a considerable variation between good tubes.

Anotherobject is to provide a method and apparatus which will function 'to group-together good tubes, although they may have different characteristics, and to separate them from bad tubes which have become run down by use.

Another object isto provide'suchapparatus including a ballast tube and. a circuit therefor so arranged thatthe-difierences between good tubes will be minimized while the difference between good tubes and bad tubes will be distinctly indicated. Q r v Further objectsyvill appear from the following description taken in connection fwith the accompanying drawings in which, I I

Figure -1 is a diagram of the basic circuit embodying this invention and Figure 2 is a complete connection-diagram of a tube testing set embodying this'invention.

In accordance with this. invention the tests indication is derivedfrom the grid plate current of thetube under test under certain. conditions imposed by the testing circuit. Considering the te'stflas applied to a single type-of tube, the vari- I ous makes of tubes of a single type will ShOW' difierent emission characteristics, While one tube willshow a highgrid-plate current another will show aconsiderably lower grid plate current under the same voltage conditions, 'both such vice.

tubes being good tubes. Both such tubes will show the same type of grid-plate current characteristiccurve although the curve of the high reading tube maybe somewhat higher than that of the. lowreading tube. A bad tube will show a very lowcharacteristic curve having a low saturation point. The present invention is .designed todis'tinguish between good and bad tubes having the above characteristics. Referring to the accompanying drawings, A in dicates'the tube under'test havingits plate and grid connected together in the ordinarymanner;

B represents a ballast tube'which is preferably a suitable triode having a long emission life. The test circuit is supplied bya transformer hav-" ing a primary winding J and three independent secondary windings K, L and M; 'The winding K isconnected to supply the filament of the tube B. The winding M is connected to supply the.

filament ofthe tube A. The winding L is connected to supplythe plate voltage for the ballast tube'B. f V

The tubes A and B are connected in series with each other and with a pair of parallel circuits, one of which extends from the filament of the tube B via a conductor 2 through a resistan'ce 'R, to the plate of thet'ube A." The other branch of the parallel circuit includes two halves, Ne and Nb of the primary winding of a transformer. The midpoint between these two halves "of the winding is connected by a conductor 3 to a point 6 between the resistance R and the filament of the tubeB. This latter transformer has a secondary winding Nc-to which analternating-current milli-ammeter 4"is connected. With the winding 5.] connected to asuitable supply 5 of alternating current, heating current I will be supplied toithe filaments of the tubes A and Band the winding L will'supply an outside voltage of, about'180 volts'to the series circuit.-;

'Ihiswlll cause a test current Itto flow in that circuit. This represents the plate current of the tube 13 andthe grid-plate current of the tube A. This current divides at the-point 6, a part thereof, I ,flowing through the half Nb of the primary winding of the indicating transformer and the remainder going through the resistance R. The resistance' R is adjustable so that the current Ib' may beadjusted for calibrating the de- These currents then recombine to flow throughfthe tube A. The flow of the current Ib through the winding'Nb causes a voltage Ea tobe indu cedin the other half Na of this winding byordin'ary.transformer'action. The voltage Es I thus inducedprovides agrid bias for the tube B.

former, the current in the secondary Winding Nc which flows through the milli-ammeter 4 will correspond to the difierence between the curents Is and Ia.

Thesoperation. oi this circuit is as ,follows.

The tube B is a permanent part of the testing set. In order to calibrate the set for a given type of tube, a good tube of that type is inserted-t asthe tube A. Preferably one ofthe lowenreading good tubes is selected for the purpose. ofcalibration. With this samplewtubez.irryzthez'circuit1.,

at A the resistance R is adjusted until a reading is obtained on the milli-ammetert at the desired portion of the scale thereof tegrepresentanormal reading for a good tube. This adjustment or the resistance R is then noted and recorded as the standard setting of thisresistance for a given type of tube. Suchha, setting is determined for each type of, tube to betestedfiiThe circuit so calibrated may now be; used to test tubes.

If new a goodtube is tested havlng the. same characteristics as, the .calibrating'tub'e, the. reading on the meter 4 will; oicours'e; be the. same.

. If atube is tested whichhasarhigherhemission than the calibrating. tubeathe. current It will be increased over the calibrating value thereofJ. This will berollowed by a correspondingnincrease in the. values ofthe current It and thecurrent inthe resistance R... .Thesetwo currents,.however, will remain in substantially-the same ratio tot each other. The increase in the current Ib will cause a slight increase in the voltage En This in turn increases the positive gridlbias of: theb-tuloe B l and, as a consequence, this tube will-assume a greaterproportion of the voltagesupplied by the winding L. Consequently, the .voltage supplied to theltube A will be slightly decreased, and; such indication ofqthe meterdi will be.-;increased.;but

slightly over; the calibrated; values Accordingly,

,all .good tubes of: this type will; show indications onthe meter 4-vvithin a comparatively narrow rangesandyrtherefore, a' rangeamayzberset *ofi upon this meter scale within which .the:indications will show good tubes. i

If now a run down tube is-placed inthe circuit at A, thecurrent Iswill be. greatly redu'cedz 'At' the same time the tube A will assume 'a greater proportion of the voltagesupplied by the winding 'L and, consequently the voltage supplied to the .rest of the circuit including theJ-tubeB is. re-

be comparatively great. Accordingly, a bad tube at A will show a low reading on the meter 4.

It will be noted that the action of the ballast tube 13 may be so controlled as to take advantage of the change in shape of the grid current characteristic. The setting of the resistance R isso adjustedth-at the normal value of Ia is approximately at the foot of the straight portionof the .grid currentncurve fort-the, tube Br Accordingly, when-the 'goodtube is "tested the current Ia will be at or above this point, while when a bad tube is tested, the current will be below that point. rBsathisnarnangement a different rate of change 'of the current Ia. is obtained When good tubes types of (tubes. -A-.multiple.-pole rotary-switch H1 is provided for.automatically-making'thes necesrsary: changes in: connections to accommodate the 'difierent-standard;tests on the idifferent'ctypes of .-.-tubes.- The.:contacts G, D, F,'G-+-l, G'--2:.and 1 Gl-3 are; stationary. and are :arranged to ;make

.contactwith any vertical row of moving contacts 111, 12, l3 .etc:, as the switch is rotated. The winding M ofthe supply.transformer=may be'provided with a'series of tapss andxa switch :wherebyrthe mvoltage supply. mayv beadjusted to suit the :type

of tube under test.. This winding is connected 1 to ally ofithe filament'terminals of. the sockets A-l to A.5 inclusive. A push "button switch -1 may contact 9 is also' connected to the indicator 8 ,.;'through themswitch ,11' When the switch -1 is edepressedmthe contact 35 thereof connects the midpoint oi the indicatingtransformer with the i'nlament oi the ballast tube B, while the contact 35 connects the arm F which is connected to the 'eommon 'cathode of all the tube sockets; to the common ground of 'the supply transformen I switch 3-1 may be provided to test for normal 'voltage; By depressing this switchthe rheostat R is cut -out and thevoltage of the-winding K is placeduupon -half of the indicating transformer and through an adjustable resistance 38 to the common'ground 40.1. The" resistance 38 is ad-' 'J'usted to give adefinite indication on 'the'meter 4 when the supply voltage is normal.

While a certain theory of action, particularly with reference to tube" characteristics, has been used in the 'foregoingdescription, it will be-understood that this is "for the purpose of clarity in" explanation; and that the invention is. not

. limited to any particular theory or .tube charactheappended claims.

"teristic', nor to any 'specificpoint onsuch characteristic; otherwise than may be called for. by

It is obvious that various changes may bemade, "within the "scope of the apnended'claim's, in the "details ofconstruction' Without; departing from .the spirit ofthis invention; it is to be understood, therefore that this invention is. not limited to: the

specific :detalisshown and/ondescribed.

Having thus describedthe invention,,fwhat', is claimed is: I a

' tubes, comprising, a ballast tube having plate,' 26

35 grid and filament electrodes, a circuit connecting for impressing a supply voltage on said circuit, 7

means in said circuit imposing on said ballast tube a grid current varying in accordance with the test current of the tube under test, and means actuated unequally by rise and fall of such grid current arranged to indicate the condition of the tube under test.

2. Apparatus for testingthermionic emission tubes, comprising, a ballast tubehaving plate, grid and filament electrodes, a circuit connecting said ballast tube with the tube under test, means for impressing a supply voltage onsaid circuit, means in said circuit traversed by an inducing current proportional tothe test current of the tube under test adapted toinduce a grid current in said ballast tube, and indicating meansactuated in proportion to the difierence between said inducing 7 current and said grid current.

3. Apparatus for testing thermionic emission grid and filament electrodes, a circuit connecting said ballast tube with the tube under test, means for impressing a supply voltage .on said circuit,

means in said circuit positively biasing said grid and imposing on said ballast tube a gridcurrent substantially proportional to the test current of" the tube under test, and indicating means differa grid comprising, passing a test current through entially affected by said grid current and said test current.

4. Apparatus for testing thermionic emission tubes, comprising, a ballast tube having plate,

said ballast tube with the tube under test, means for impressing a supply voltage on said circuit, a transformer in said circuit having a primary winding, an adjusting circuit paralleling a portion of said winding, said parallel circuits being connected to be traversed bythe test current of the tube under test, another portion of said wind,-

tube a grid current induced by the current in said first portion of said winding, and indicating means afiected differentially by said currents in said different winding portions.

-5. Apparatus for testing thermionic emission tubes, comprising, a ballast tube having plate, grid and filament electrodes, a circuit in which said tubes and an indicating circuit are arranged in series, means for impressing a supply voltage on said first circuit; said indicating circuit in- "cluding a transformer winding, current-regulatingmeans connected across a portion of said winding, and another portion of saidwinding beingconnectedtc impose its induced voltage upon fthe grid circuit of said ballast' tube; and indieating means connected to be actuated diiferentially by the currents in said winding portions.

-6. The method of 7 testing thermionic emission tubes, involving the use of a ballast tube having a grid comprising, passing a test current through thetube'and the ballast tube in, series while si.

multaneously imposing-a positive voltage on the grid. of the ballasttube', measuring a differential between the grid current,- and an oppositely phasedLcOmponent of said test current, and comparing the measurement with a similar measure ment taken on a standard tube to indicate the quality'oi the tube under test. I

1 7. The method of testing "thermionic emission tubes, involving the use of a ballast tube havin I "current to impose an opposite changein the proportion of saidimpressed voltage absorbedby the tube under test, measuring adifferential between the resulting grid current of the ballast tube and an oppositely phased component of said test current, and comparing the measurement with a similar measurement taken on a standard tube to indicate the quality of the tube under test.

VICTOR H. LAUGHTER' ing being connected to impose upon said ballast l A 

